Interpretive Summary: Pecan is North America’s most valuable native tree-nut, with worldwide cultivation and substantial production in the United States and Mexico. This tree crop is attacked by a wide variety of disease and insect pests that greatly reduce tree productivity if improperly managed. In 2002, the pecan root-knot nematode, Meloidogyne partityla, was found on pecan in the southeastern United States and associated with stressed trees exhibiting dead branches in the upper canopy and/or typical Mouse-ear associated foliar symptoms. A ring nematode, Mesocriconema xenoplax, was also detected in the soil samples. Determining the interactions between M. partityla and M. xenoplax on pecan growth, nematode reproduction, and incidence of mouse-ear needs to be investigated.
A long-term field microplot study (i.e., 37 months) was conducted at ARS Byron, GA to determine the interaction between the ring and pecan root-knot nematode as it relates to nematode reproduction, tree growth and mouse-ear disorders in Desirable pecan. Results indicate that the presence of root-knot nematode in suppressed reproduction of ring nematode in soil. Additionally, the pecan root-knot nematode suppressed tree growth and increased incidence of mouse-ear severity in pecan more than ring nematode.
These data provide useful insights into the interactive relationships between two plant parasitic nematodes in pecan disease complexes and the need in developing appropriate root-knot nematode management strategies in pecan.

Technical Abstract:
The interaction between Meloidogyne partityla and Mesocriconema xenoplax on nematode reproduction and growth of Desirable pecan was studied in field microplots. Meloidogyne partityla suppressed reproduction of M. xenoplax, whereas the presence of M. xenoplax did not affect the population density of M. partityla second-stage juveniles in soil. Above-ground tree growth, as measured by trunk diameter, was reduced in the presence of M. partityla alone or in combination with M. xenoplax as compared with the uninoculated control trees 32 months following inoculation. The interaction between M. partityla and M. xenoplax was significant for dry root weight 37 months after inoculation. The synergistic effect indicates that the presence of the two nematode species together caused a greater reduction in root growth than M. xenoplax alone, but not as great a reduction as compared to M. partityla alone. Mouse-ear severity in pecan leaves was increased in the presence of M. partityla as compared with M. xenoplax and the uninoculated control. Meloidogyne partityla appears to be a more dominant parasite than M. xenoplax on Desirable pecan.